UDC 548.5:546.26-162:62-987
T. V. Kovalenko*, V. Yu. Klochok, V. A. Burchenya, S. O. Ivakhnenko, V. V. Lysakovsky, O. O. Zanevsky, O. M. Suprun
V. M. Bakul Institute of Superhard Materials, NAS of Ukraine, Kyiv, Ukraine
*tetiana.v.kovalenko@gmail.com
NRNT-crystallization of diamond on a seed using carbon solvents formed by powder metallurgy methods (pp. 3-12)
Thermobaric formation of carbon solvent alloys at high pressures (4–6 GPa) and temperatures (1200–1300 °C) was used to grow structurally perfect single crystals of diamond in the region of thermodynamic stability. It is shown that the formation of samples with minimal (from 2.49 to 4.50%) porosity values ensures a stable distribution of elements in the growth volume even in the presence of large differences in the density of elements. For comparison, the results of experiments on the formation of solvent alloys by the methods of powder metallurgy and direct isostatic pressing with subsequent sintering, as well as by the methods of hot pressing of powders, which are common in practice, are presented. It is shown that the samples obtained by classical methods have relatively large values of final porosity and cannot be used further as carbon solvent alloys during the directional growth of diamond single crystals at high pressure and temperature.
Keywords: diamond, NRNT crystallization, carbon solvents, powder metallurgy.
UDC 620.22:621.315.612.8
M. M. Prokopiv*, O. V. Kharchenko
V. M. Bakul Institute of Superhard Materials, NAS of Ukraine, Kyiv, Ukraine
*keramtex@ukr.net
A new ceramic material with a gradient structure obtained from an exothermic mixture of ZrO2‒Al‒C in contact with a eutectic mixture of 68Al2O3–32ZO2 in the process of free sintering (pp. 13-20)
The microstructure, chemical composition and properties of a ceramic heterophase material of dispersion-strengthened type based on ZrС–Al2O3–ZrO2 with a gradient layer up to 100 μm thick of the eutectic structure (% (by weight)) based on 68Al2O3‒32ZrO2 were studied. The material was obtained from an exothermic mixture of ZrO2‒Al‒С in contact with a eutectic mixture of 68Al2О3‒32ZrO2 in the process of simultaneous free sintering in an argon environment at a temperature of 1700 °С for 30 min of isothermal holding. It was shown that the introduction of a small amount of oxides (MgO, TiO2, Cr2O3, SiO2, Fe2O3, etc.) into the exothermic and eutectic mixture made it possible to reduce the Tevt from 1915 °С to the technological temperature of 1700 °С with complete densification of the exothermic mixture. According to the results of chemical analysis, the main structure includes two equivalent matrix phases – ZrC and Al2O3, with dispersed inclusions mainly in the carbide phase. The structure of the gradient layer, which is additionally doped with metal oxides, is quasi-eutectic, its chemical composition corresponds to the chemical composition of the initial eutectic mixture – 68Al2O3‒32ZrO2. The thickness and profile of the gradient structure layer obtained during the sintering process depend on the thickness and profile of the eutectic powder slip applied to the surface of the pressed sample from the exothermic mixture. The boundary between the main and gradient structures is perfect. The hardness of the material of the main and gradient structures is 18.7 and 16.5 GPa, respectively, and the crack resistance KIс is 5.8 and 4.2 MPa m0.5, respectively.
Keywords: ceramic material, eutectic, gradient structure, Al2O3, ZrO2, properties.
UDC 621.921.34:621.793:546.76
Qingzhu Ge1,*, Meng Yan2, Yang Jiang1, Yonghong Wang1, Junwu Liu1
1Department of Materials Science and Engineering, Hefei University of Technology, Hefei, P.R. China
2State Key Laboratory of Solidification Processing, Center of Advanced Lubrication and Seal Materials, Northwestern Polytechnical University, Xi’an, Shaanxi, P.R. China
*804806306@qq.com
Characterization of molten salt chromium coating on micron-scale diamond particles (pp. 21-34)
The influence of technological parameters on the structure and morphology of molten salt chromium coating on micron-scale diamond particles, which was used to modify their surface topography, was investigated. The coating characteristics were studied using scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. It was shown that molten salt provides a high rate of chromium deposition on the diamond surface. A complex coating is formed when the chromium content reaches 6% (by mass) and the residence time in the salt bath exceeds 40 min. Increasing the temperature to 950 °C in the case of using the molten salt method reduces the likelihood of cracks on the surface of the coatings. At a heating temperature of 1050 °C, graphite can be detected in the coating. Adding 6–10% (by mass) chromium to the salt mixture and heating to 950 °C allows you to achieve an integrated coating with a strong connection with the surface of the diamond particles. The thickness of the resulting coating is from 312 to 826 nm.
Keywords: molten salt method, aluminum particles.